1. Field of the Invention
The present invention relates to a semiconductor memory device and a driving method thereof; and more particularly, to a semiconductor memory device and a driving method thereof that are capable of improving a noise characteristic of a voltage signal provided to a memory cell of the semiconductor memory device.
2. Description of the Related Art
In recent years, the capacity and speed or memory chips, which are used as memory devices in electronic systems, have increased. Furthermore, various attempts to increase memory capacity per unit area and to drive the memory more rapidly have been made.
FIG. 1 is a schematic view of a general conventional semiconductor chip 10. Referring to FIG. 1, the semiconductor chip 10 includes an I/O region 11, which includes an input/output circuit for sending/receiving data signals and control signals, etc. to/from an outside system, and cell regions 12, which include memory cells for storing the data.
Generally, the semiconductor chip 10 has a structure in which the I/O region 11 is disposed in a central region of the semiconductor chip 10 and the cell regions 12 are disposed on both sides of the I/O region 11. The I/O region 11 includes one or more pads PAD, where voltage signals, data signals, and control signals, etc. are inputted from the outside system via the pads PAD. In order to store or read the data, the voltage signals, the data signals, and the control signals are supplied to the cell regions 12 through the input/output circuit of the I/O region 11.
In the semiconductor chip 10, the area of the cell regions 12 occupies most of the chip area, and paths of the power supply voltage and the ground voltage supplied to the memory cells pass through the I/O region 11 in the center of the semiconductor chip 10. In a general case, the power supply voltage and the ground voltage are applied to a semiconductor package on which the semiconductor chip 10 is mounted through solder balls disposed on an outer surface of the semiconductor package. However, in this configuration, a feed/sink path of the voltage signals becomes relatively long, which hampers performance characteristics of the chip 10.
FIG. 2 is a cross-sectional view of a general conventional semiconductor package that illustrates a path of a voltage signal transferred to the semiconductor chip. Referring to FIG. 2, the semiconductor package may include one or more semiconductor chips having a stacked structure, and a package substrate 30 for mounting the stacked semiconductor chips.
FIG. 2 illustrates a case where two semiconductor chips are stacked as an example of a conventional semiconductor package. In addition, the semiconductor package illustrates an example in which one or more semiconductor chips are packaged in a wafer stack form. The two semiconductor chips include I/O regions 11 and 21, respectively, which are positioned in the center of the package substrate 30, and cell regions 12 and 22 which are disposed on both sides of the I/O regions 11 and 21, respectively.
A power supply voltage or a ground voltage that is transferred from one or more solder balls mounted on the bottom surface of the package substrate 30 through the I/O regions 11 and 21 to reach the cell regions 12 and 22. The power supply voltage or the ground voltage is inputted to an input/output circuit included in the I/O regions 11 and 21 and is then supplied from the input/output circuit to the cell regions 12 and 22. An arrow indicated in FIG. 2 shows a path through which the voltage signal from the solder balls attached to the outer surface of the package substrate 30 is supplied to the cell region 12.
In order to supply the voltage signal from the I/O regions 11 and 21 to the cell regions 12 and 22, aluminum wiring, which has a relatively large resistance, is generally used. As FIG. 2 shows, this path can become relatively long. This length coupled with the large resistance of the wiring path can generate noise in the voltage signal provided to the cell regions 12 and 22. As a result, the performance of the entire memory system deteriorates.